The gas condensate produced in conjunction with the pressure gasification of coal contains various substances which pollute the environment, such as free NH.sub.3 or combined NH.sub.3, H.sub.2 S, HCN, and mono- and polyvalent phenols in addition to fatty acids, chlorides, fluorides, tars, oil and dust. That gas liquor cannot readily be discarded because it contains valuable substances, which can be recovered, as well as many noxious substances, which must be removed from the gas liquor except for low residual contents in order to avoid an unnecessary pollution of the underground water and river water or to enable a further use thereof.
The tars and oils are removed by separation and filtration and are separately sold or burned.
Dust is returned to the pressure gasification process and enters the ash.
Free ammonia (NH.sub.3) is driven off and concentrated or burned.
CO.sub.2 and H.sub.2 S as well as HCN are also driven off and supplied, e.g., to a plant for producing sulfur.
The monovalent phenols are preferably extracted to a few ppm and are recovered. (See LURGI Handbook 1970, Chapter 2.1, published by LURGI, Frankfurt-on-Main; Erdol und Kohle, 13, 1960, pages 252-257.)
Upon the removal of the monovalent phenols, part of the polyvalent phenols are removed too. The remainder remains in the water together with the fixed NH.sub.3, which is mainly combined with fatty acid or is present as chloride and fluoride. The poor extraction of the polyvalent phenols is due to the fact that the partition coefficients are, on an average, lower by about one power of ten than the partition coefficients for monovalent phenols.
A disproportionately large solvent circulation would be required for a recovery also of the polyvalent phenols.
The extraction plant is normally followed by a biological afterpurification plant. These processes for removing the remaining polyvalent phenols are uneconomical and as far as the biological processes are concerned require great experience as regards the provision and preservation of the biologically active sludge.
If the phenols are recovered in an alkaline process, the resulting phenolate must be dissociated.